Cutting elements, as for example cutting elements used in rock bits or other cutting tools, typically have a body (i.e., a substrate), which has an interface end or surface. An ultra hard material layer is bonded to the interface surface of the substrate by a sintering process to form a cutting layer, i.e., the layer of the cutting element that is used for cutting. The substrate is generally made from tungsten carbide-cobalt (sometimes referred to simply as “cemented tungsten carbide,” “tungsten carbide” or “carbide”). Cemented tungsten carbide is formed by dispensing carbide particles in a cobalt matrix, i.e., cementing tungsten carbide particles together with cobalt. To form the substrate, tungsten carbide particles and cobalt are mixed together and then heated to solidify. The ultra hard material layer is a polycrystalline ultra hard material, such as polycrystalline diamond (“PCD”), polycrystalline cubic boron nitride (“PCBN”) or thermally stable product (“TSP”) material such as thermally stable polycrystalline diamond.
To form a cutting element having an ultra hard material layer such as a PCD or PCBN ultra hard material layer, diamond or cubic boron nitride (“CBN”) crystals are placed adjacent the cemented tungsten carbide body in a refractory metal enclosure (e.g., a niobium can) and subjected to high temperature and high pressure so that inter-crystalline bonding between the diamond or CBN crystals occurs, forming a polycrystalline ultra hard diamond or CBN layer. Cobalt from the tungsten carbide substrate infiltrates the diamond or CBN crystals and acts as a catalyst/binder in forming the PCD or PCBN. An additional catalyst or binder material may also be added to the mixture of diamond or CBN particles to assist in inter-crystalline bonding. The process of high temperature heating under high pressure is known as high temperature high pressure sintering process (“HTHP” sintering process).
Metals such as cobalt, iron, nickel, manganese and alike and alloys of these metals have been used as the catalyst material for the diamond or CBN, to assist in inter-crystalline bonding between the diamond or CBN particles. As mentioned above, this catalyst material infiltrates the ultra-hard material layer from the substrate during HPHT sintering, and additional catalyst material may be added to the ultra-hard powder mixture prior to sintering. However, if the catalyst material is unevenly distributed throughout the ultra-hard particles, or if the catalyst material from the substrate does not fully infiltrate the ultra-hard layer, the sintered ultra-hard layer may include pockets or regions where inter-crystalline bonding did not take place. Thus, an even distribution or infiltration of catalyst material in the ultra-hard layer is desired to achieve efficient and effective sintering and to produce a uniform PCD or PCBN microstructure.
The ratio of the amount of catalyst material to ultra-hard material also affects the HTHP sintering process. Too little catalyst material (too low a ratio) results in poor sintering and an absence of inter-crystalline bonding. Too much catalyst material (too high a ratio) can interfere with the bonding between ultra-hard particles and degrade the properties of the cutting layer. Additionally, the amount of catalyst blended into the ultra-hard particle mixture prior to sintering should be carefully controlled to avoid the accumulation of too much catalyst material in the ultra-hard layer when the catalyst from the substrate infiltrates the ultra-hard layer during HPHT sintering. Without a balanced ratio of catalyst material and ultra-hard material, sintering is less efficient, the resulting PCD or PCBN microstructure is less uniform, and performance of the cutting element is degraded.
In the prior art, catalyst material has been added to the ultra-hard particle mixture by powder blending, that is, by dry mixing the catalyst (such as cobalt) and the ultra hard particles (such as diamond) together into a powder blend. The prior art also includes methods of coating ultra-hard particles with a catalyst material in an effort to achieve a uniform distribution of the catalyst material in the ultra-hard particle mixture prior to sintering. For example, U.S. Pat. No. 5,759,216 discloses a method of manufacturing a diamond sintered body, including coating the surface of each diamond particle with a sintering assistant agent. The preferred method disclosed in this patent is coating by electroless plating. Other prior art methods include chemical vapor deposition, physical vapor deposition, and atomic layer deposition. Many of these methods include complicated steps such as sensitizing the surface of the ultra-hard particles prior to depositing the metal plating.
In these prior art methods, the amount of catalyst coated on the ultra-hard particles may depend on the surface area of the ultra-hard particles. Smaller ultra-hard particles have a larger surface area per unit volume as compared to larger particles. When these smaller particles are coated with a catalyst material, the resulting ratio of catalyst material to ultra-hard particles can be hard to control. There are many variables that have to be controlled in these prior art methods in order to obtain the desired ratio of catalyst material to ultra-hard particles, and as a result it is difficult to achieve consistent coatings of the desired thickness. Thus, in the prior art, it has been difficult to achieve efficient and complete sintering of very fine ultra-hard particles, such as diamond or CBN particles with a nominal grain size less than 8 micron. Another problem with very small particles is the difficulty in uniformly wetting the surface, which causes inconsistent results in coating the surface with a catalyst. Thus, prior art coating methods often result in large variation in the amount of catalyst coated on these small ultra-hard particles, making it difficult to precisely control the amount of catalyst provided.
Some prior art methods of distributing catalyst material onto the ultra-hard particles utilize other additives in addition to the catalyst material. For example, electroless plating requires the addition of a plating catalyst such as palladium or tin. This additional material introduces impurities that degrade the sintering process and interfere with the formation of crystals in the ultra-hard layer. For example, the presence of tin in the sintered compact deteriorates performance due to the low melting point of tin. U.S. Pat. No. 6,541,115 attempts to address this issue by providing a palladium-free coating. However, this reference requires a separate activation layer comprising silver, which is deposited on the diamond before the catalyst layer is coated. Accordingly, this method still introduces additional impurities into the coating process.
Accordingly, there is a need for a method of depositing a catalyst material on an ultra-hard particle that provides a uniform distribution of catalyst material and reduces the impurities introduced into the ultra-hard particle mixture prior to sintering.